Staple acrylic yarns for threads and cordage



United States Patent "ice 3,492,805 STAPLE ACRYLIC YARNS FOR THREADS AND CORDAGE Witold R. Kocay, Stamford, Conn., and James B. Denmark and Allen H. Farr, Decatur, Ala., assignors to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Feb. 16, 1968, Ser. No. 705,946 Int. Cl. D02g 3/02 U.S. Cl. 57140 9 Claims ABSTRACT OF THE DISCLOSURE Acrylic yarns suitable for use as sewing thread, cord or twine, or for further processing into sewing thread or cordage, and having an acceptably high tenacity, with minimally acceptable qualities of fibrillation and elongation, are produced by spinning staple acrylic fibers of generally low tenacity and high elongation into yarn of generally low tenacity, and by substantially stretching the spun yarn under thermal conditions.

BACKGROUND OF THE INVENTION This invention relates to a process for the production of acrylic yarns suitable for use as thread, sewing thread, cord or twine, or for further processing into sewing thread, cordage and the like; and more particularly, to a process for imparting high tenacity and low elongation to yarns from acrylic staple fibers and to the product thereof.

The textile industry has long been without a suitable and economically produced acrylic sewing thread or cordage. Previous attempts to supply such products have demonstrated that continuous filament acrylic yarn is too costly to produce, and is too brittle when produced from filaments of sufficiently high tenacity. The use of yarns spun from acrylic staple fibers has also failed to provide an acrylic cord or thread of acceptable standards because acrylic fibers having sufficiently high tenacity and low elongation to provide, in the finished product, a satisfactory sewing thread, cord or twine, cannot survive the conventional spinning process. Twisting of this high tenacity low elongation staple during conversion into yarns results in substantial breakage of fibers. On the other hand, when the spun yarn is made from low tenacity high elongation staple of a quality such as to resist breakage during the spinning process, it is of insufficient tenacity and of excessive elongation to provide a satisfactory finished product of sewing thread, or cordage. In short, those qualities of acrylic fiber which are consistent with efiicient yarn spinning processes are inconsistent with the use of the spun yarn for sewing thread or cordage. Although specific requirements will vary with the intended use of the end product, it may be conservatively estimated that acceptable ranges of strength and elongation in a yarn to be used as thread, sewing thread, cord or twine, or in cordage products generally, as recognized in the textile industry, will be limited by a minimum tenacity of approximately 1.6 grams per denier and a maximum elongation of about 20%. The preferred elongation of such yarns is about 10%.

SUMMARY OF THE INVENTION It has been found that yarns of acrylic fiber, spun from relatively low tenacity, high elongation acrylic staple, can be thermally drawn or hot stretched up to about 70%, thereby increasing the tenacity of the fiber, at the same time decreasing the ultimate yarn elongation and the yarn denier. The resulting product is suitable for use as,

3,492,805 Patented Feb. 3, 1970 or for further processing into thread, sewing thread, cord, twine, and other cordage products, commercially acceptable qualities having been achieved Without damage to the fiber during the spinning process.

Accordingly, it is an object of this invention to provide a process for the production of an acrylic thread, sewing thread, cord or twine from staple acrylic fibers.

Another object of this invention is to provide yarns of acrylic fiber having tenacity and elongation qualities suitable for use as thread, sewing thread, cord or twine, or for use in further processing into sewing thread of cord age products generally.

These and other objects of this invention will become apparent from the ensuing detailed description of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT By acrylic fibers is meant fibers produced from acrylonitrile polymers. By acrylonitrile polymer is meant polyacrylonitrile, copolymers and inter polymers of acrylonitrile, and blends of polyacrylonitrile and copolymers of acrylonitrile with other polymerizable mono-olefinic materials, as well as blends of polyacrylonitrile and such copolymers with small amounts of other polymeric materials, such as polystyrene. The types of acrylonitrile fibers, the variations and blends of polymers used in the production of these fibers as well as production techniques, are well known in the art, and are described in such patents relating to the production of acrylonitrile containing fibers, as, for example, U.S. Patent 3,088,793.

Any acrylic fibers produced from acrylonitrile homopolymers and copolymers, with variations and blends, as described generally above, are suitable for use in ac cordance with this invention. Commercially, acrylic fibers may be manufactured by wet spinning of acrylonitrile polymers from organic solvent solutions. The method briefly entails dissolving the acrylonitrile polymer in a suitable organic solvent or inorganic salt solution to produce a spinning solution, extruding the spinning solution through a multiorifice spinning jet into a coagulating bath to form a plurality of filaments, washing the filaments to remove residual solvent, drawing the filaments to achieve molecular orientation, and finally drying the washed filaments to remove moisture. The fibers may also be produced by dry spinning wherein the solvent is removed from the spinning solution by evaporation.

The acrylic staple fibers suitable for conventional yarn spinning and for heat stretching in accordance with this invention, preferably have a denier from about 3 to 25 per filament, and a staple length from about 1 to 8 inches. We have found that 15 denier filaments possess a good balance of physical properties, are easily spun into yarn on conventional woolen or worsted textile machinery, and function well in the practice of this invention. Staple of 25 or higher denier may also be used if care is taken in the operation of the yarn spinning apparatus. Similarly, lower denier fibers may be converted into yarns on either woolen or cotton processing machinery using conventional techniques. Fiber staple length is necessarily determined by the method selected for yarn spinning, and may vary from about 1 inch up to about 10 inches. In a preferred embodiment of this invention, wherein 15 denier fibers are spun to yarns on worsted equipment, the preferred staple length is from 3 to 8 inches.

A description of the end products of this invention, and the methods of producing these products, except as detailed herein, must be for the purpose of this application, clothed in generalities. Thread, sewing thread, cords, twine and cordage products generally are of an infinite number of varieties and involve many different processes and combinations thereof. Volumes have been written on the subject. Thread, as used herein, means a slender strand or strands of a specialized type of yarn used for some particular purpose such as basting, sewing, darning, embroidery work, etc. Commonly it is a cord made of two or more yarns twisted or plyed and then finished for a definite purpose. Cordage, as used herein, is a general term which includes banding, cable, cord, rope, string, and twine made from fibers. The term twine, as used herein, is an aggregate of parallelized fibers or yarns compacted into a twisted structure of continuous length, 'which is used essentially for tieing or binding. The term cord, as used herein means an aggregate of yarns braided or twisted into a structure of continuous length, generally less than in diameter, with a compacting of fibers and a structural balance to maintain compactness. Rope is a flexible, twisted yarn-strand structure, usually greater than A in diameter, structurally balanced to maintain compactness. As suggested by these definitions, and by virtue of the various twisting, plying and braiding operations, and finishing processes, it is easily seen that depending upon the type of yarn spun and the method of spinning, its physical arrangement, and whether or not and when the yarn will be subjected to a finishing process, all determined by precise nature of the end product, the above described heat stretching of yarns may or may not result in the finished product. For example, the heat stretching step may well be the ultimate step in the production of a sewing thread or twine. It may be the penultimate step in the production of a thread and followed by a finishing step. Or it may be, as in the production of rope, that the heat stretched acrylic yarn may be subjected to yet further twisting and plying, as well as finishing steps, in the preparation of the end product.

Since fiber denier, staple length, and method of yarn spinning are not critical to the practice of this invention, and since variations thereof are within the capabilities of those skilled in the art of yarn spinning and textile processing, the remainder of this specification will be directed toward describing one preferred embodiment to illustrate the practice of this invention.

Specifically, the following description and examples will be concerned with the production of acrylic sewing threads, cords, twine and the like from denier acrylic fiber cut to a staple length of about 6 inches and spun to yarn on the worsted system. Typically, these fibers have a tenacity range of from about 1.7 to 2.4 grams per denier and an elongation range of from about to 45 percent. The yarns obtained from these fibers are usualiy of low to medium tenacity, or within a tenacity range of from 1.2 to 1.5 grams per denier, and have a relatively high elongation of 20 to percent.

The thermal stretch employed in accordance with the instant invention may be a dry heat stretch or a steam stretch, the latter being preferred, having been observed to produce slightly superior results. Yarn temperature may vary from about 86 C. to about 235 C. Preferred begin to thermally degrade or to assume a tacky composition. The preferred temperature range is from safely above the second order transition temperature to safely below the thermal degradation temperature. These temperatures, while critical, are not finite; and it can only be said with respect to the full range that it is a conservative operable range for the heat stretch, but that slight variations below the stated minimum or above the stated maximum will not necessarily yield patently unacceptable results. Permissible variations of heat exposure time and distance need only conform to the stretch capacity of the particular filament involved and lend the heat stretch process of this invention well to a continuous process whereby heat is applied in a tube through which the fibers move continuously, the fiber entry speed being slower than the fiber exit speed.

The amount of stretch imparted in accordance with this invention may be as much as 70%. However, stretch ratios as low as 1.20 have produced acrylic twines of acceptably high tenacity and low elongation.

The following examples further illustrate the preferred embodiment of this invention wherein an acrylic twine is produced from 15 denier acrylic staple fibers. Variations in denier, staple length, and method of yarn spinning and drawing are contemplated and considered to be within the scope of the invention which is not to be limited by the examples but only as specifically set forth in the appended claims.

EXAMPLE I A 4 ply twine of 2/ 1 cc. acrylic spun yarn of 15 denier per filament, cut to a 6" staple, with S twist at 6 turns per inch and with a steam setting on the twist was subjected to a heat stretch in accordance with this invention. The acrylic fiber, initially produced from a copolymcr containing 93% acrylonitrile and 7% vinyl acetate, was cut to staple and spun on a worsted system in accordance with the figures shown in the left column. Elongation, breaking strength and tenacity, as shown in the third, fourth and fifth columns are the results of standard tests run on the cord after heat stretching.

TABLE I Breaking Total Elongation, strength, Tenacity,

Stretch ratio denier percent gms. gms./den.

It will be observed that percent elongation at stretch ratios of less than 1.2 is increased rather than decreased and is beyond maximum acceptable requirements for sewing thread.

EXAMPLE II The 15 denier acrylic staple described in Example I was spun on the worsted system and plied into a sample having a nominal yarn count of 3.5/4. This yarn was hot stretched as shown at various stretch ratios to obtain the properties shown.

TABLE 2 Breaking Yarn strength, Tenacity, Elongation, U Knot Yarn denier number, cc. grns. g./d. percent lbs.

Original 6,650 3. 2 4 8, 200 1. 23 29 14. 0 1:20 stretch rat 5, 000 3. 6/4 9, 800 1. 66 10 16. 2 1:30 stretch ratio 5, 450 3. 9/4 8, 800 1. 61 13 16. 8 1:35 stretch ratio 5, 060 4. 2/4 9,030 1. 78 11 15. 8 1:60 Stretch ratio 3, 040 4. 7/4 9,700 3. 19 9 15. 5

70 EXAMPLE III temperatures are from C. for steam stretching to about C. for dry heat stretching. The temperature range of 86 to 235 C. reflects a minimum below which there is an unacceptable amount of fiber breakage during the stretch, and a maximum above which the first stages of fiber decomposition begin to appear; that is, the fibers Thermal stretch conditions Control, 3.5/4 cc.

A, 3.5/4 cc. Hot Stretched 1.30 at 173 C. B, 3.5/4 cc. Steam Stretched 1.30 at 100 C.

6 3. The process of claim 1 wherein said yarn is heated to from about 86 C. to about 235 C.

4. The process of claim 1 wherein the yarn is heated in steam to about 100 C.

5. The process of claim 1 wherein the heat stretched Control, /3 cc. 5

C 5 /3 cc Hot Stretched 130x at yarn is heat set at a temperature above about 150 C. D, 5 /3 ca Steam stretched 130x at 6. In a process for the preparation of yarns from acrylic Control 4 staple fibers wherein said staple fibers are spun into yarn 6/4 Hot s h d 130 at 173 c by conventional textile methods, the improvement of F, 6/4 cc. Steam Stretched 1.30 at 100 C. heating said yarn to from about 86 C. to about 235 C.

TABLE 8 Breaking U knot Yam Tenacity, strength, Elongation, strength, Condition number, cc. Yarn denier gms./den. gms. Percent gms.

Control, 3.5/4 cc- 3. 2/4 5, 55s 1. 2 s, 091 27 7, 202 A 4. 1 4 5, 202 1. 7 s, 681 10 7, 571 3. 9/4 5, 437 1. 7 s, 054 13 s, 187 4. 8/3 3, 305 1. 4 4, 726 24 4, 154 6. 1/3 2, 533 2.0 5, 250 13 4, 172 0. 0 3 2, 652 1. s 4, 753 10 4, 580 5. 5 4 3, 205 1. 5 4, 972 28 3,813 8. 1 4 2, 625 2. 1 5, 573 11 3, 01s 7. 5/4 2,796 2. 1 5, 032 13 3, 684

The twine produced according to the preceeding examples, although entirely satisfactory for its intended use, was found to have high boiling water shrinkage. For many applications, such as sewing awnings, sandbags, and the like, this shrinkage is of no consequence. Where application is such that the sewn article is to be subjected to elevated temperatures such as in washing and drying operations, the acrylic twine may be heat set at elevated temperatures, preferably above 150 C., in order to reduce the potential shrinkage of the yarn and thereby avoid puckering seams.

As stated in the body of the specification, the preceeding examples illustrate a preferred embodiment of the present invention employing high denier acrylic fiber. It is contemplated that other deniers and acrylic fiber compositions other than that specifically described may be similarly processed with equally efiective results, and such fibers are considered with the broad scope of the present invention.

We claim:

1. A process for the production of acrylic yarns of sufiiciently low elongation and sufiiciently high tenacity for use as thread, sewing thread, cord and twine and in cordage products comprising the steps of spinning acrylic staple fibers into a yarn, heating said yarn and concurrently stretching said yarn from about to about 70%.

2. The process of claim 1 wherein said yarn is stretched about 30%.

and concurrently stretching said yarn from about 20% to about whereby the tenacity of said yarn is substantially increased, and the elongation is substantially decreased.

7. Yarn spun from acrylic staple fibers, said yarn having a minimum tenacity of about 1.6 g./d. and a maximum elongation of about 20%.

8. Sewing thread comprised of acrylic staple fibers, said thread having a minimum tenacity of about 1.6 grams/denier and a maximum elongation of about 20%.

9. Cordage comprised of acrylic yarn having a minimum tenacity of about 1.6 grams/ denier and a maximum elongation of about 20 percent.

References Cited UNITED STATES PATENTS 2,455,173 11/1948 Hi t 287l.3 XR 2,628,405 2/1953 Wentz 2871.3 2,766,505 10/1956 Weiss.

2,976,578 3/1961 Virgil 1937 3,175,029 3/1965 WhalOn et al 2871.3 XR 3,302,385 2/1967 Ruddell et al. 1946 3,330,896 7/1967 Fujita et al 57140 XR STANLEY N. GEREATH, Primary Examiner WERNER H. SCHROEDER, Assistant Examiner US. Cl. X.R. 57-157 

